Electrical connector

ABSTRACT

A device for forming an electrical connection between a plurality of elongate electrical conductors comprises an electrically insulating sleeve, and contained within the sleeve a resiliently deformable tapering coil and a quantity of fusible polymeric material, the device being arranged so that the elongate electrical conductors may be connected by twisting them into the coil so that at least part of the coil is deformed and heating the device so that at least some of the fusible polymeric material melts and then, when solidified, substantially binds the coil in its deformed state.

This invention relates to electrical connectors for forming electricalconnections between elongate conductors.

Simple electrical connectors which contain a screw thread, enablingwires and the like to be connected by screwing them into the connectorare well known. Whilst these simple connectors provide a quick and easymethod of producing an electrical connection, they often suffer fromunreliability due to the connection not being secure; wires and the likeoften work loose over a period of time, due to strain on the connection.In addition, these types of connectors are often not sealed from theenvironment and this leads to corrosion. In order to overcome theseproblems, more sophisticated connectors have been proposed, such as forexample the types of connectors described in international patentapplication No. WO 92/00616. These connectors contain, in addition to ascrew thread connector, a quantity of solder which provides a permanentsoldered connection once the connector has been heated for a sufficientperiod of time for the solder to melt. The connectors are alsoenvironmentally sealed by means of a heat recoverable sleeve which mayadditionally contain thermoplastic sealing rings. Whilst theseconnectors perform excellently, in order to form the solder connectionthey require a degree of heating which is either inappropriate or tootime consuming for some applications.

According to one aspect of the present invention, there is provided adevice for forming an electrical connection between a plurality ofelongate electrical conductors, which comprises an electricallyinsulating sleeve, and contained within the sleeve a resilientlydeformable tapering coil and a quantity of fusible polymeric material,the device being arranged so that the elongate electrical conductors maybe connected by twisting them into the coil so that at least part of thecoil is deformed and heating the device so that at least some of thefusible polymeric material melts and then, when solidified,substantially binds the coil in its deformed state.

According to another aspect of the invention, there is provided a methodof forming an electrical connection between a plurality of elongateelectrical conductors, which comprises:

(i) twisting one end of each elongate electrical conductor into atapering coil of a device according to the invention so that at leastpart of the coil is deformed;

(ii) heating the device so that at least some of the fusible polymericmaterial melts; and

(iii) allowing the device to cool so that the molten polymeric materialsolidifies and substantially binds the coil in its deformed state.

The device and method according to the invention generally enable theformation of reliable electrical connections since deformation of thetapering coil by twisting elongate electrical conductors into itnormally causes the coil to grip the conductors due to its resilience.Because of this, the coil may be referred to as a `gripping coil` or aconnecting coil`. The coil may, for example, be deformed in this way byat least part of it being radially expanded. Alternatively oradditionally the deformation may comprise axial extension of at leastpart of the coil. It is believed that substantially binding the coil inits deformed state by the solidification of the polymeric materialnormally causes the coil's grip on the elongate conductors to bemaintained; it also normally renders the coil substantially rigid. Thesetwo effects appear generally substantially to prevent the elongateconductors working loose from the coil over a period of time and hencenormally lead to reliable electrical connections.

According to one preferred embodiment of the invention, at least some ofthe fusible polymeric material that is contained within the sleeve ofthe device is located between the internal surface of the sleeve and theexterior of the coil. When, in use, the polymeric material is melted, atleast some of the molten material normally flows and conforms to theexterior of the coil and therefore, when solidified, substantially bindsthe coil in its deformed state. The fusible polymeric material of thispreferred embodiment of the invention may, for example, be in the formof an insert having any one of a variety of shapes, such as for examplea ball, a pellet or a ring at least part of which surrounds at leastpart of the tapering coil. Where a ring of material is used, preferablyit has a substantially frustoconical shape which generally conforms tothe taper of the coil. More preferably, however, at least some of thefusible polymeric material has the form of a layer located on at leastpart of the internal surface of the sleeve. Most preferably, the layeris located on substantially the entire internal surface of the sleeve.

According to another preferred embodiment of the invention, the fusiblepolymeric material is located beyond an open end of the coil of thedevice. When, in use, the polymeric material is melted, at least some ofthe molten material normally flows into the interior of the coil andtherefore, when solidified, substantially binds the coil in its deformedstate. Preferably, the fusible polymeric material of this embodiment ofthe invention has the form of a ring, through which the elongateconductors may extend. When, in use, at least part of such a ring offusible polymeric material is melted and subsequently solidifies, atleast some of the material may help to seal the electrical connectionfrom the environment.

The fusible polymeric material according to the invention preferablycomprises a hot-melt adhesive. The material may, for example, be formedfrom an olefin homopolymer or from a copolymer of an olefin with otherolefins or ethylenically unsaturated monomers. Preferred examplesinclude high, medium or low density polyethylene or ethylene copolymerswith alpha olefins, especially C3 to C8 alpha olefins, vinyl acetate orethyl acrylate. Alternatively, the material may be formed frompolyamides, polyesters, halogenated polymers and the like. Preferredpolyamides include those having an average of at least 15 carbon atomsbetween amide linkages, for example those based on dimer acids and/ordimer diamines. Examples of such adhesives are given in U.S. Pat. Nos.4,018,733 to Lopez et al and 4,181,775 to Corke, the disclosures ofwhich are incorporated herein by reference. Particularly preferredpolyamides are those which are sold under the trade name `VERSALON` byGeneral Mills Chemicals Inc. of Minneapolis, USA. Alternatively, thefusible polymeric material may comprise a thermoset material orcomposition. For example, the material may comprise one or more phenolicresins, amino resins, epoxy resins, or mixtures thereof, together withone or more curing agents, for example having reactive amine groups. Itis preferred for the thermoset material to be in particulate form, forexample as described in U.S. Pat. No. 4,896,904, the disclosure of whichis incorporated herein by reference.

For some applications of the device according to the invention it isadvantageous for the fusible polymeric material to have been blendedwith a quantity of metal particles, especially silver particles, therebyforming an electrically conductive composition. This may often beparticularly advantageous for embodiments of the invention wherein atleast some of the electrically conductive composition flows into theinterior of the coil when the polymeric material is molten. Examples ofsuitable electrically conductive compositions include those described inInternational Patent Application, Publication No. WO91/06961, thedisclosure of which is incorporated herein by reference.

The coil of the device according to the invention may be formed from anyof a variety of materials, for example, the coil may be formed from aplastic material. Preferably, however, the coil is formed from metal,for example a substantially pure metal or a metal alloy. Preferredmetals are steel, especially spring temper steel, and copper, especiallyhard temper copper.

The tapering coil of the device according to the invention is preferablyformed from wire (metal wire or `plastic wire`). The wire may generallyhave any cross-section which will allow a plurality of elongateelectrical conductors to be connected by twisting them into the coil.Preferably, however, the cross-section of the wire is such that the wirehas a ridge extending along its length which provides the coil with aninternal screw thread. This has an advantage in that, where the hardnessof the wire of the coil is greater than that of the elongate conductors,twisting the conductors into the coil in the same direction as the screwthread will normally result in the wires being screwed into the coil,due to the internal screw thread of the coil digging in to the elongateconductors. Most preferably the wire has a polygonal cross section, andin this case at least one of the angled portions of the cross sectionmay form the ridge extending along the length of the wire.

The tapering coil and the fusible polymeric material of the device arecontained within an electrically insulating sleeve. According to aparticularly preferred embodiment of the invention, at least part of thesleeve is dimensionally heat-recoverable. A dimensionallyheat-recoverable sleeve is an article which has a dimensionalconfiguration which may be made substantially to change when subjectedto heat treatment. Usually, such articles recover, on heating, towardsan original shape from which they have previously been deformed, but theterm `heat-recoverable`, as used herein, also includes articles which,on heating, adopt a new configuration, even if they have not previouslybeen deformed.

The heat-recoverable sleeve may comprise a heat shrinkable article madefrom a polymeric material exhibiting the property of elastic or plasticmemory as described, for example, in U.S. Pat. Nos. 2,027,962, 3,086,242and 3,597,372. As is made clear in, for example, U.S. Pat. No.2,027,962, the originally dimensionally heat-stable form may be atransient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a pre-formed dimensionally heat-stablearticle is deformed to a dimensionally heat-unstable form in a separatestage.

The sleeve is preferably formed from a polymeric material. Preferredmaterials include: low, medium or high density polyethylene; ethylenecopolymers, e.g. with alpha olefins such a 1-butene or 1-hexene, orvinyl acetate; polyamides, especially Nylon materials, e.g. Nylon 6,Nylon 6.6, Nylon 11 or Nylon 12; and fluoropolymers, e.g.polytetrafluoroethylene, polyvinylidenefluoride,ethylene-tetrafluoroethylene copolymer or vinylidenefluoridetetrafluoroethylene copolymer.

For some applications, the device according to the invention may includea terminal portion, which preferably comprises a lug portion and ahollow shank. The terminal portion of the device may be connected to thetapering coil in any appropriate way; for example it may be soldered tothe coil, the shank of the terminal portion may be crimped or crushedonto the coil, or the coil may be screwed into the shank of the terminalportion.

In the broadest aspect of the invention, the device includes aresiliently deformable tapering coil. The device may therefore include asingle tapering coil so that a stub splice may be formed between aplurality of elongate conductors inserted into one end of the sleeve,the other end of the sleeve for example being closed, especially bymeans of a sealing ball as described in International Patent ApplicationNo, WO91/11831, the disclosure of which is incorporated herein byreference, or by means of the end of the sleeve being flattened so thatopposing portions of the sleeve are squashed together and held in thisway by means of polymeric material fused between the opposing portionsof the sleeve. Alternatively, however, the resiliently deformable coilmay taper from two opposite directions to an intermediate region ofminimum diameter. This form of device may therefore be used to form anin-line splice between a plurality of elongate electrical conductors.Another form of device according to the invention may also achieve thispurpose: according to this embodiment, the device includes a secondresiliently deformable tapering coil connected to the first taperingcoil by connecting means. The connecting means may take any appropriateform, for example it may comprise a substantially cylindrical elementwhich is provided with two or more protrusions or grooves which arecapable of interlocking with the windings of the coils. The two coilsmay have the same or opposite handedness. It is also possible for thetwo coils to be rotatable with respect to each other.

Three forms of device according to the invention will now be describedby way of example with reference to the accompanying drawings, in which:

FIG. 1 an isometric projection, partly in section, of a device accordingto the present invention;

FIG. 2 is an isometric projection, partly in section, of a second formof device according to the invention and several insulated wires;

FIG. 3 is an isometric projection of an electrical connection betweenseveral insulated wires formed by means of the device shown in FIG. 2;

FIG. 4 is an isometric projection, partly in section, of a third form ofdevice according to the invention, and several insulated wires; and

FIG. 5 is an isometric projection of an electrical connection betweenseveral insulated wires formed by means of the device shown in FIG. 4.

Referring to FIG. 1 of the accompanying drawings, a device 1 for formingan electrical connection between a plurality of elongate electricalconductors comprises a dimensionally heat-recoverable electricallyinsulating sleeve 3, formed from cross-linked Nylon 11 or Nylon 12,containing a resiliently deformable tapering coil 5 of hard tempercopper wire of square cross-section and a sealing ball 7 formed fromirradiated or non-irradiated polyethylene. The sleeve 3 has a layer offusible polymeric material 9 located on its internal surface, thematerial comprising a polyamide hot-melt adhesive.

Referring now to FIG. 2, a second form of device 11 according to theinvention comprises a dimensionally heat-recoverable sleeve 3 having alayer of fusible polymeric material 9 located on its internal surface,the sleeve containing a tapering coil 13 of hard temper squarecross-section copper wire which is connected to a second tapering coil15, also of hard temper square cross-section copper wire, by means of asubstantially cylindrical copper connecting element 17. The sleeve 3also contains two rings of fusible polymeric material 19, formed frompolyamide hot-melt adhesive, each located beyond one of the open ends ofthe coils 13 and 15.

The device 11 may be used to form an in-line electrical splice between aplurality of insulated wires 25, as shown in FIG. 3. In order to formthe splice, the ends of the wires 25 (each having an exposed length ofconductor) are inserted into the device 11 through either open end 27 ofthe sleeve 3 and through the respective ring of fusible polymericmaterial 19 and twisted into the relevant tapering metallic coil 13 or15. The two coils 13 and 15 have opposite handedness, so that theoperator may either hold the device 11 stationary and twist the wires 25into the coils or he may hold the wires stationary and twist the deviceonto them. The wires 25 are preferably twisted into each coil 13 or 15in the same direction as the windings of the coil, so that they areeffectively screwed into the device 11. Twisting the wires firmly intothe coils will normally cause at least part of each coil to deform, forexample by radial expansion and therefore grip the wires due to itsresilience.

In order to bind the coils 13 and 15 in their deformed state and to sealthe splice from the environment, the device 11 is heated, for example bymeans of an infra-red heater, a hot air gun, or a naked flame (acigarette lighter may be used). Heating the device 11 causes the fusiblepolymeric material of the layer 9 and the rings 19 to melt and whencooled and solidified the material binds the coils in their deformedstate. Heating the device 11 also causes the sleeve 3 to recover aboutthe insulated wires 25, and this, together with at least some of thefused polymeric material of the rings 19, seals the splice from theenvironment.

FIG. 4 shows a device 27 according to the invention, which is similar tothe device shown in FIG. 1, the only difference being that this devicehas a terminal portion 29 instead of a sealing ball 7. The terminalportion 29, which is formed from pressed copper or aluminium, comprisesa lug portion 31 and a hollow shank 33. The shank 33 contains therelatively narrow end region 35 of the tapering copper coil 5.

Also shown in FIG. 4 are several insulated wires 25, which are shown inFIG. 5 inserted into the device 27. Similarly to the splice of FIG. 3,the electrical connection shown in FIG. 5 has been formed by twistingthe wires 25 into the tapering copper coil 5 and heating the device 27in order to melt the fusible polymeric material 9 and to cause thesleeve 3 to recover about the wires.

We claim:
 1. A device for forming an electrical connection between aplurality of elongate electrical conductors, which comprises anelectrically insulating sleeve, and contained within the sleeve aresiliently deformable tapering coil and a quantity of fusible polymericmaterial, the device being arranged so that the elongate electricalconductors may be connected by twisting them into the coil so that atleast part of the coil is deformed and heating the device so that atleast some of the fusible polymeric material melts and then, whensolidified, substantially binds the coil in its deformed state.
 2. Adevice as claimed in claim 1, wherein at least some of the fusiblepolymeric material is located between the internal surface of the sleeveand the exterior of the coil.
 3. A device as claimed in claim 1, whereinat least some of the fusible polymeric material has the form of a layerlocated on at least part of the internal surface of the sleeve.
 4. Adevice as claimed in claim 1, wherein the fusible polymeric material islocated beyond an open end of the coil.
 5. A device as claimed in claim1, wherein the fusible polymeric material comprises a hot-melt adhesive.6. A device as claimed in claim 1, wherein the fusible polymericmaterial has been blended with a quantity of metal particles, therebyforming an electrically conductive composition.
 7. A device as claimedin claim 1, wherein the coil is formed from metal.
 8. A device asclaimed in claim 1 wherein the coil is formed from a wire.
 9. A deviceas claimed in claim 8, wherein the wire has a ridge extending along itslength which provides the tapering coil with an internal screw thread.10. A device as claimed in claim 9, wherein the wire has a polygonalcross-section.
 11. A device as claimed in claim 1, wherein at least partof the sleeve is dimensionally heat-recoverable.
 12. A device as claimedin claim 1, which includes a terminal portion comprising a lug portionand a hollow shank.
 13. A device as claimed in claim 1, wherein theresiliently deformable coil tapers in two opposite directions to anintermediate region of minimum diameter.
 14. A device as claimed inclaim 1, which includes a second resiliently deformable taperinggripping coil connected to the first tapering coil by connecting means.15. A method of forming an electrical connection between a plurality ofelongate electrical conductors, which comprises:(i) twisting one end ofeach elongate electrical conductor into a tapering coil of a device asclaimed in claims 1 to 14, so that at least part of the coil isdeformed; (ii) heating the device so that at least some of the fusiblepolymeric material melts; and (iii) allowing the device to cool so thatthe molten polymeric material solidifies and substantially binds thecoil in its deformed state.